Prothrombinase assay for cell surface phosphatidylserine exposed in IFN-2a–induced cells.

Cells were incubated 18 hours with either 0 (open symbols) or 1000 IU/mL (closed symbols) IFN-α2a. After induction with IFN-α2a, cells were challenged with calcium ionophore (open and closed squares) and prothrombinase activity measured as a function of time after addition of A23187 (abscissa). Open and closed circles denote results for identically matched cells omitting A23187. Upper panel shows results for cell line HT1080 receiving 5 μM A23187; lower panel shows results for human umbilical vein endothelial cells receiving 10 μM A23187. Results (mean ± SD) are plotted from a single experiment representative of similar experiments performed at least 3 times with each cell type.